1. Field of the Invention
This invention relates generally to mechanical end face seals for sealing between a housing and a relatively rotating shaft and more particularly to such seals having a metal diaphragm which provides axial loading of the seal rings and also acts as a secondary seal between one of the seal rings and its associated housing or shaft.
2. Background Art
Mechanical end face seals which provide a fluid-tight seal between a housing and a relatively rotating shaft find general application to a variety of devices, such as liquid pumps, slurry pumps, dry mixers and numerous other devices. Low cost end face seals are used, for example, in a number of high volume applications such as automobile water pumps. Applications involving other process fluids are also common.
Face seals usually comprise two seal rings, having opposed sealing faces, one of which rotates relative to the other. A biasing force is normally provided to urge one seal ring toward the other and to bring the two sealing faces into sealing relation. Secondary seals in some form seal each ring to its associated shaft or housing.
An example of a seal using a coil spring to provide the biasing force can be found in U.S. Pat. No. 3,282,235. A seal using a wave spring is shown in U.S. Pat. No. 4,754,981. These seals use some type of elastomeric component for providing the secondary sealing function. The latter seal is unitized, in that it can be installed into a pump as a unit or sub-assembly.
Seals are known in which the axial bias and the secondary seal between the movable ring and its associated housing or shaft is provided by an annular metal diaphragm or bellows. Such seals generally have higher temperature capability than those using an elastomeric secondary seal as well as potentially having better uniform circumferential loading. Examples of such seals are found in U.S. Pat. Nos. 2,189,197; 3,203,704; 3,332,692 and 3,575,424.
Seals using diaphragms of formed metal are not without complexity. The diaphragm or bellows must be connected to the seal ring and the housing or shaft with which it is associated in fluid-tight relation. These connections pose manufacturing and assembly problems.
Formed metal bellows have traditionally taken the shape of a truncated cone which, when the seal is installed, is placed in compression. Such shapes generally provide a high spring rate which can necessitate high initial face loading with consequent wear. Such seals may experience short life due to loss of adequate closing force as face wear progresses. Also, face loading varies significantly depending on diaphragm deflection. Leakage sometimes results from relaxation of the diaphragm through axial seal ring movement.
Simplicity of installation and removal of seals often dictate cartridge type arrangements which allow all of the seal elements to be preassembled and installed as a unit. There is also the desire to minimize the axial length of the seal assembly thereby minimizing the overall length requirement of the shaft. Reduction in shaft length simplifies bearing requirements and reduces the overall length of the pump or other device in which the seal is utilized.
The present invention incorporates an annular metal diaphragm in a seal assembly such that axial loading of the axially movable seal ring is applied by placing the diaphragm in tension. The diaphragm configuration provides greater flexibility and a resultant spring rate which insures adequate closing force over an acceptable range of axial displacement. This flexibility permits lower initial preload and therefore accommodates a narrow face width configuration. The narrow face width configuration, in turn, avoids potential thermal distortion problems.
In the preferred form, the relationship of the component parts results in a cartridge configuration. This embodiment utilizes a sleeve and retainer, each associated respectively with one of the seal rings. The metal diaphragm forms one closure wall of the cartridge. The entire seal assembly is essentially defined by the axial extent of the metal body of the primary ring retainer with the seal rings contained between a wall of the retainer and the metal diaphragm.